Murphy is batting .133 (2 for 15) with one triple and two RBI through six spring games.
"Exciting day for all of us," general manager John Mozeliak said. "A lot went into this. ... We made a very conscious effort over the past year to start to understand the Cuba market, to start to understand how we could put our fingerprints on this. All along we targeted middle infielders if that was something we could do to improve our organization.
"We feel pretty confident this is a good fit for the organization. One of the things we're always trying to do is add depth."
The 23-year-old Diaz is expected to open the season in the minors, possibly Double-A, and will make his spring debut once the Cardinals are certain he's physically ready for game-speed competition.
"We plan on being patient with him," Mozeliak said. "He hasn't played baseball in really over a year and a half competitively. We're not looking for him to put his fingerprints on the major-league team tomorrow. We can give him time to develop and let him from a talent standpoint take his time to get back to where he was and I think from our organizational standpoint that's a great fit for us at this time."
The Royals also optioned
"Last year, the pitch a lot of times was a ball out of his hands," manager Walt Weiss said. "He's getting swings and misses with it now. And he's throwing his changeup more."
"As of right now, he’s going to be in right field," McClendon said. "During the course of the season, it’ll be a day-to-day thing."